1. Field of the Invention
The present invention relates to a semiconductor device, a solid-state image sensor, methods of manufacturing the same, and a camera.
2. Description of the Related Art
There is available a method of forming an interlayer insulating film on an etching stopper and then forming a contact hole in the interlayer insulating film so as to stop etching at the etching stopper. In this method, the etching stopper is etched so as to penetrate the etching stopper exposed at the bottom of the contact hole after forming an opening in the interlayer insulating film.
Japanese Patent Laid-Open No. 2012-182426 describes a method of, after forming a silicide layer in a transistor, forming an insulating film including a silicon nitride film, forming an interlayer insulating film made of silicon oxide on that, and then forming a contact hole in the insulating film and the interlayer insulating film.
A general silicon nitride layer has low hydrogen permeability when it undergoes an insufficient annealing process. According to “Journal of Applied Physics, V86, pp 2237-Duterium transport through device structures, P. J Chen and R. M. Wallace”, the permeability of the silicon nitride layer increases by undergoing an annealing process at a temperature of 900° C. or higher.
As in the example described in Japanese Patent Laid-Open No. 2012-182426, when forming the silicide layer in the transistor, a processing temperature after forming the silicide layer is restricted from the viewpoint of protecting the silicide layer. For example, when the silicide layer is formed by a cobalt silicide, the upper limit for the processing temperature is about 850° C. Since the silicon nitride layer used as an etching stopper for forming the contact hole is formed after a silicidation step, it is not desirable to perform the annealing process on the silicon nitride layer at the temperature of 900° C. or higher. For this reason, the silicon nitride layer is maintained at low hydrogen permeability. When the hydrogen permeability of the silicon nitride layer is low, the supply of hydrogen to the transistor is restricted by the silicon nitride layer. Therefore, the termination rate of a dangling bond is decreased, resulting in degradation in transistor characteristics such as a subthreshold characteristic and mobility.
In a current solid-state image sensor, the speedup of a peripheral circuit becomes more important as the number of pixels increases. Therefore, a process which degrades the subthreshold characteristic, mobility, and the like closely related to the speedup should be avoided.